Second-order model for rotary traveling wave ultrasonic motors

Ultrasonic motors are compact actuators with high precision and high stall torque. They feature a friction-based actuation principle and offer an alternative to standard actuators such as direct current motors. However, their nonlinear dynamics, the presence of load-dependent dead zones and the difficulty to control low speeds often prohibit their use. Those issues can be overcome by proper design of a controller. In this work, a novel model for a rotary traveling wave ultrasonic motor, the USR60 from Shinsei, is presented. The novel discontinuous model takes into account the dependency of the motor´s velocity on the frequency of the traveling wave, the phase difference of the underlying standing waves and the load-dependent dead zone width. The model is identified with data obtained from a testbed and may serve as a foundation for the design of a variety of controllers.